Previous to this invention, to get a meaningful fluid sample a person was required to go to the wellhead everytime to get the first fluid sample, wait the required periods of time between samples before getting a second and possibly several thereafter for a meaningful or desired sample or samples. This was very time consuming, costly, and unreliable. It was difficult to achieve, among other problems. These problems prompted the design of the disclosed sampler for automatic capture for analysis produced oil well fluid, for example, at specific time intervals, for detection of injected chemical solutions, for determining the arrival of many chemical species, as polymers, surfactants, tracers, or treating chemicals at the well. The oil sample may likewise be analyzed for the presence of surfactants. Particularly, the time of arrival and the time variation of concentration of the injected chemical solution at the producing well may be determined.